Which inspection method should be avoided on vessels containing 5% H2S?

The most appropriate choice for inspection methods that should be avoided on vessels containing 5% H2S is the hammer testing method. Hammer testing, often referred to in a broader sense as impact testing or the "ping" test, involves striking the surface of the vessel and listening to the sound produced to assess the material condition.

In environments where hydrogen sulfide (H2S) is present, there is a significant risk of embrittlement and stress corrosion cracking. As a result, the integrity of the vessel's material can be compromised. When performing hammer testing in such conditions, you may inadvertently overlook serious flaws or damage because the method relies heavily on the operator's experience and subjective judgment regarding sound rather than concrete, quantifiable data. Moreover, the physical impact of hammer testing may exacerbate existing flaws, especially in materials weakened by H2S.

Other inspection methods, such as visual inspection, ultrasonic testing, and magnetic particle testing, are generally more reliable and suitable for assessing the condition of pressure vessels in H2S environments, as they can provide more detailed and quantitative data regarding wall thickness and the presence of surface or subsurface flaws without adding stress to the material.